This is done pretty simple you have to Open Chrome Browser extension Interface:

(Go to Right corner 3 Dashes) Tools menu -> Settings -> Extensions

Or if you prefer to do it manually with a command like me type in URL address bar:

chrome://chrome/extensions/

Usually plugin files for Chrome that are installable comes in Custom-Plugin-namer.JS or Whatever-plugin-name.CRX.

Next take the plugin (from any folder it is located or right from Chrome’s download folder or wherever the plugin you want to install that is not otherwise available via Chrome Web Store and(drag and drop) – place it into Extensions opened window.

You’ll be prompted to confirm installation of the extension, just as if you had installed it from the Chrome Web Store.